The only thing that I am aware of that they could be talking about, is the "Mortgage Interest Credit Certificate" apparently still available in some states.

https://www.ncsha.org/resource/mortgage-credit-certificate-program-qa/

Form 8396 is the form. I have only had one client use it (about 10 years ago) and it is currently not available in my state of  Washington. I am not fully up on all the background, but it is somehow sponsored /  participated in by various state housing programs.